A novel multifunctional ionic liquid additive 1-(3-amino-3-oxopropyl)-3-vinylimidazolium bis(trifluoromethylsulfonyl)amide ([PIVM][TFSA]) is designed to enhance the electrochemical performance of silicon-based lithium ion batteries. Due to its multifunctional groups, this ionic liquid has the potential to improve silicon based lithium ion batteries. The basic group binds water and thereby keeps the formation of hydrogen fluoride (HF) at a low level. The vinyl group of the ionic liquid contributes to the formation of a uniform passivating solid electrolyte interphase (SEI) film in silicon-based lithium ion batteries. The cycle life of the silicon-carbon half-cells with this ionic liquid is improved greatly. After 50 cycles, the capacity retention of half-cells with presence of ionic liquid is obviously higher than that of cells without ionic liquid. Electrochemical methods are used to analyze the effect of the ionic liquid. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) are used to detect the structure and components of the SEI layer.